Table tennis ball manufacture



June 12, 1945- G. H. PERRYMAN 'TABLE' TENNIS BIALL MANUFACTURE Filed Aug. 12/ 1943 w m. m w.

Patented June 12, 1945 TABLEfliznhmsnau muraorngcg I" George" HJRerrymaIr,

r i i This;invention-frelates to a. means and; method for making table tennis balls and: similarihollow objects suchas-are-made fromthermoeplastic sheet material such as nitro-celluloseori cellulose acetate; and has for its object the provision of means by which improved balls. can be speedily and: economically manufactured; 1

" As iswell'known, the conventional table-tennis joint of exceptional strength is provided between will produce a the twohalves, and one which 'seam' of scarcely perceptible nature; a The invention further contemplates'an im;-

proved method ofmaking the balls whereby means are provided to direct the flow of the adjacent solvent-softened flange material of the halves of the ball to the interior of the ball,

whereby said solvent-softened material is disposed over the interior of the joint between the two halves and an exceedingly strong joint between the halves is the result.

Another object of the invention is to provide an improved die means by whichthe ball halves are pressed together so that the solvent-softened material is caused to be displaced inwardly or toward the interior of the ball to thereby build up an interior bridge over and around the joint between the ball halves. I

In the accompanying drawing, wherein an embodiment of the invention is disclosed, Fig. 1 is a plan view of a strip of the sheet material from which the balls are formed, showing four ball halves formed thereon preparatory to being joined to four similar halves; Fig. 2 is a sec-, tional View on the line 2--2 of Fig. 1, looking in the direction of the arrows; Fig. 3' shows two ball halves in readiness to be placed with their solvent-coated flanges in contact, and the die means for applying pressure on the flanges; Fig.- 4 shows how the die means operates to compress the flanges together and cause an inward displacement of the solvent-softened portions of the flanges; Fig. 5 shows how the flanges are later mp ication anemia mdiseaarmieeszae I 1; (cl. i-1"5 i 1c);f' j v I I I *"lfablewtenniss balla'are usually made from.

ziit-raacelll1lose;. often. known under: the trade name; of; @elluloidfir' or; from celluloseawait-a Q1. similar:thermoplastic:material. I n;carrying out the-method of thepresent:inventionand formin halveeLof the ball, a .r-iumb'er' of these halves; such-asefour, ate..=formed: in a strip of the sheet material while.- it; is relatively: soft, by, the. opera= 'tion-of aisuitabl'e die; 1m Figs. 1: and 2: arershown fouzi ball'halve's t pressed "from. a: strip; 2 and; in readiness to bew cut 'therefrom, ifit :isadesired. to

,make-theballsone aha-time. In such:cases,nthe

halvs may bw out out of the strip I 1 along: the dotted linesto. provide each-zballrhalf so. cut

out, with the flange 4. However, in the; interest of -speedy produetion," it will be found. desirable to' simiiltaneously make four .or moreballs, and

s'edoing, two strips such asare shown at' I i in Figs. '1" and"- 2;=andeach-- containing four ball I hates-=- ar praeee together 'in I the manner here: 'aftrje blamed- 1 r F" 'Ajc'oa ting; of? a solvent'psuch as acetone,- ethyl *acetateior any other suitable solvent, is then applied 'to the" outer facesbetween the formed ball halves, and the hemispheres are then placed together with their solvent-coated flanges in contact to form the spheres. In Fig. 3, the position 'of two hemispheres just prior to being placed together, is

shown, and'while the following description will apply to the making of a single ball, it will be understood that it applies to the simultaneous manufacture of a number of balls, such as for example, four as shown in the strip I. Before pressure is applied upon the flanges in the manner hereafter described, itis necessary that any air'trapped within the ball to be formed and/or the material of the ball itself, shall be subjected to heat so that when the subsequent cooling of the material of the ball itself, and/or the air trapped within the ball occurs, the pressurewithin the ball is materially reduced and the tendency of the ball halves to separate, dueto in-,

terior pressure while the material of the joint is in a semi-plastic condition, will be obviated.

trimmed away, and Fig. 6 is a sectional view through the completed ball. v,

This heating of the material of the ball itself and/or the air within the ball, can be done in several ways, one satisfactoryway being to subject the ball halves to the action of heat just before placing them together and. before sealing to form the ball. Or the ball :halvesmay be heated after placing them together but before compressing'them. By this;latter method, the expanding air within the ball will cause the ball to S oft-he' flanges; or those parts of the two strips I which are located breathe" in the seam and allow the pressure to escape before the ball halves are compressed together by the annular sealing die.

When the heated halves are placed together as above described, the flanges 4, with their solvent-coated faces 5 in contact, are subjected to pressure between two annular sealing dies 6 and 1. Each of these two dies is of annular or tubular form, so that it fits closely around a ball half, and since the two dies are inaccurate axial alignment they will, when brought toward one another, automatically and accurately align the two ball halves.

It will be noted in Figs. 3 and 4 that each of the dies 6. and 1 is provided with an inclined operative surface, that shown at 8 being provided on the face of the die 6, while a similar surface is shown at 9 on the die 1. When the two dies 6 and I are brought toward one another, they compress the flanges 4 between the surfaces 8 and -9. It will be noted that these co-operating die surfaces 8 and 9 diverge in a direction toward the interior of the ball, and as shown in Fig. 4, the result of pressure applied to the flanges'4 between these surfaces is to cause a considerable portion of the solvent-softened portions of the flanges to be displaced or forced inwardly toward the interior of the ball and caused to be built up over .the interior surface of the seam in and around the joint between the ball halves on the inside of the ball. The displaced portions of the flanges 4 thus form a bridge in over the seam or joint between the two ball halves on the inside of the ball and acts to securely unite the halves into a sphere.

When the halves have been united by the drying of the solvent, the then united flanges 4, 4

' are cut or trimmedoff, this being done by the dies [2, l2 illustrated in Fig. 5, which come together -to such an extent as to nearly penetrate the flanges 4, without these dies actually contacting with one another, permitting the flanges 4 to be easily stripped off after having been treated by the dies I2, l2. The ball is thereafter the halves scarcely imperceptible.

It will be seen from the foregoing that while the ball is composed of halves united by a butt joint, the joint, formed in the manner described, is an exceedingly strong one due to the disposition of the solvent-softened material being displaced inwardly and being built up on the interior of the ball and actually across the seam. The effect of the spread of the solvent-softened material is to provide a bridge across the joint to securely unite the halves. It will be further noted that the ball has no overlapping parts so that good balance is attained since the relatively small and uniformly built-up interior ring of the solvent-softened material is insufficient to cause any material effect on the balance of the ball.

What I claim is:

. In the method of making table tennis balls and the like from thermo-plastic material, the steps of forming ball halves each provided with a radially extending circumferential flange, softening the adjacent surfaces of the flanges only with sufficient solvent to enable the material of said surfaces to be displaced under pressure and placing said surfaces in contact, subjecting the flanges only of the ball halves to pressure [by pressure means which confines said pressure solely to the flanges without contacting with or imposing pressure on any other parts of the ball halves, whereby the solvent-softened contacting faces of the flanges are the only parts of the ball halves affected by said pressure, said pressure forcing the solvent-softened portions of the flanges inwardly and into the interior of the ball halves to build up and extend over and coat the joint between the ball halves.

G. H. PERRYMAN. 

